The invention relates to a double-tube vibration damper.
In a vibration damper which is suitable to take up wheel guidance forces, that is to say is to take up radial forces, it is known (Fed. German Patent application No. 30 08 707) to arrange a piston ringe in an annular recess of the piston, the axial extent of the piston ring amounting to a multiple of the ring wall thickness. In order to achieve a good sealing effect and an exact guidance of the piston ring and thus of the piston in relation to the inner wall of the cylinder under all operating conditions, the piston ring is pressed, without radial play, with a relatively great pressing force against the inner wall of the cylinder. Accordingly the piston ring is subjected to high radial forces and must consist of a material favorable to slippping, in order to keep the friction resistance low.
Furthermore in vibration dampers it is known (French Pat. No. b 2,088,644) to provide at least one substantially axially proceeding groove in the inner wall of the cylinder, for stroke-dependent damping force variation, which forms with the piston ring a by-pass cross-section for the working chambers separated by the piston. As a result of the high pressure differences between the working chambers occurring in double-tube vibration dampers, especially in the traction phase, the piston ring is to be made relatively rigid, so that it does not yield into the cylinder groove due to the high pressures building up in the piston ring groove. If the rigidity of the piston ring is inadequate the by-pass cross-section and thus also the required damping effect are modified in an undesired manner, and no unambiguous control edge is formed for the by-pass cross-section.
The present invention is directed towards provision of a double-tube vibration damper which is suitable for taking up wheel guidance forces, which forms an unambiguous control edge for the by-pass passage formed by an axial groove in the cylinder and which guarantees a satisfactory sealing effect between the working chambers and good guidance of the piston, with minimum friction, even when taking up wheel guidance forces.